The NACRE Thermonuclear Reaction Compilation and Big Bang Nucleosynthesis

TL;DR

This paper assesses how the NACRE nuclear reaction data compilation influences Big Bang nucleosynthesis predictions, focusing on uncertainties and their impact on light element abundance estimates and cosmological parameters.

Contribution

It introduces new methods for estimating nuclear reaction rate uncertainties and evaluates their effects on BBN predictions and cosmic baryon density constraints.

Findings

NACRE rates do not significantly change central BBN predictions.

Uncertainty estimates can be refined to reduce light element prediction errors.

Derived limits on the baryon-to-photon ratio consistent with CMB measurements.

Abstract

The theoretical predictions of big bang nucleosynthesis (BBN) are dominated by uncertainties in the input nuclear reaction cross sections. In this paper, we examine the impact on BBN of the recent compilation of nuclear data and thermonuclear reactions rates by the NACRE collaboration. We confirm that the adopted rates do not make large overall changes in central values of predictions, but do affect the magnitude of the uncertainties in these predictions. Therefore, we then examine in detail the uncertainties in the individual reaction rates considered by NACRE. When the error estimates by NACRE are treated as 1\sigma limits, the resulting BBN error budget is similar to those of previous tabulations. We propose two new procedures for deriving reaction rate uncertainties from the nuclear data: one which sets lower limits to the error, and one which we believe is a reasonable description of the present error budget. We propagate these uncertainty estimates through the BBN code, and find that when the nuclear data errors are described most accurately, the resulting light element uncertainties are notably smaller than in some previous tabulations, but larger than others. Using these results, we derive limits on the cosmic baryon-to-photon ratio $\eta$, and compare this to independent limits on $\eta$ from recent balloon-borne measurements of the cosmic microwave background radiation (CMB). We discuss means to improve the BBN results via key nuclear reaction measurements and light element observations.